I live close to montreal and we have a lot of environmentally conscious people here.
While a nice idea, instead of reusing my grocery bags as bin liners, I have to buy bin liners as well as the occasional bag when I forget. The net result is more plastic waste for me.
Now I have to buy bin liners, as well as the occasional reusable plastic bag. The reusable plastic bag has 4x the plastic content of the disposable ones.
And yes, having to buy a new reusable bag if you forgot yours is frustrating. Which makes it memorable, and less likely to happen again - though that may be more of a personal thing.
If you have a lot of extra reusable plastic bags, perhaps you could push your local grocery store to put in a "take a bag/leave a bag" box? To ensure they get put to good use
5-10 years ago in the grocery store line, myself and half the people in front of me were bringing our own reusable grocery bags. I feel guilty acknowledging this, but we all just seemed to... stop. Because it was a mild hassle, and the novelty wore off. I can't remember the last time I've seen someone with with their own bags, and I imagine that younger store clerks would be confused by them.
We're still concerned about plastic (that worry comes and goes like a pendulum). We just got bored and lost our attention span for one of the most direct things we can do to reduce plastic.
10-15 years ago, myself and most of my political peers were more upset about Guantanamo Bay than plastic or climate change. Nothing ever changed there, but I can't recall the last time I've heard it mentioned. The average anti-war protestor of the post-9/11 years probably understands little to nothing about U.S. action in Syria over the past decade.